媒体基础 - 如何从交叉栏中选择输入

晚上好

我正在尝试使用Media Foundation将一个小的视频捕获DLL放在一起，该DLL在很大程度上改编自SimpleCapture和CaptureEngine SDK示例。当我的捕获源是我的内置网络摄像头时，整个事情都很好用。

问题是当我尝试使用具有多个输入（s-video，复合和立体声音频）的外部USB图像采集卡时，没有预览流。我有一个使用 DShow 接口的功能，它似乎可以成功更改横杆上的选定输入（通过运行函数后查看 AMCAP 中的选项进行验证）但是我根本无法预览设备。

是否有从交叉栏选择输入的媒体基础方法？或者如果没有，您能否建议下面的交叉条输入选择代码可能存在什么问题：

HRESULT CaptureManager::doSelectInputUsingCrossbar(std::wstring deviceName, long input) 
{

IGraphBuilder *pGraph = NULL;
ICaptureGraphBuilder2 *pBuilder = NULL;
IBaseFilter* pSrc = NULL;
ICreateDevEnum *pDevEnum = NULL;
IEnumMoniker *pClassEnum = NULL;
IMoniker *pMoniker = NULL;
bool bCameraFound = false;
IPropertyBag *pPropBag = NULL;

bool crossbarSet = false;
HRESULT hr = S_OK;
if (!(input == PhysConn_Video_Composite || input == PhysConn_Video_SVideo))
{
    return S_FALSE;
}

// Create the Filter Graph Manager.
 hr = CoCreateInstance(CLSID_FilterGraph, NULL,
    CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
if (SUCCEEDED(hr))
{
    // Create the Capture Graph Builder.
    hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL,
        CLSCTX_INPROC_SERVER, IID_ICaptureGraphBuilder2,
        (void **)&pBuilder);
    if (SUCCEEDED(hr))
    {
        pBuilder->SetFiltergraph(pGraph);
    }
    else return hr;
}
else return hr;
//////////////////////////

// chooses the default camera filter
hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC,
    IID_ICreateDevEnum, (void **)&pDevEnum);
if (FAILED(hr))
{
    return E_FAIL;
}
// Create an enumerator for video capture devices.
if (FAILED(pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pClassEnum, 0)))
{
    return E_FAIL;
}
if (pClassEnum == NULL)
{
    CheckHR(hr, "Class enumerator is null - no input devices detected?");
    pDevEnum->Release();
    return E_FAIL;
}

while (!bCameraFound && (pClassEnum->Next(1, &pMoniker, NULL) == S_OK))
{
    HRESULT hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void**)(&pPropBag));
    if (FAILED(hr))
    {
        pMoniker->Release();
        continue;  // Skip this one, maybe the next one will work.
    }
    // Find the description or friendly name.
    VARIANT varName;
    VariantInit(&varName);
    hr = pPropBag->Read(L"Description", &varName, 0);
    if (FAILED(hr))
    {
        hr = pPropBag->Read(L"FriendlyName", &varName, 0);
    }
    if (SUCCEEDED(hr))
    {
        if (0 == wcscmp(varName.bstrVal, deviceName.c_str()))
        {
            pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pSrc);
            bCameraFound = true;
            break;
        }//if
        VariantClear(&varName);
    }
    pPropBag->Release();
    pMoniker->Release();
}//while
pClassEnum->Release();
pDevEnum->Release();
if (!bCameraFound)//else
{
    CheckHR(hr, "Error: Get device Moniker, No device found");
    goto done;
}

hr = pGraph->AddFilter(pSrc, L"video capture adapter");
if (FAILED(hr))
{
    CheckHR(hr, "Can't add capture device to graph");
    goto done;
}

///////////////

IAMCrossbar *pxBar = NULL;
hr = pBuilder->FindInterface(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Interleaved, pSrc, IID_IAMCrossbar, (void **)&pxBar);
if (FAILED(hr))
{
    hr = pBuilder->FindInterface(&PIN_CATEGORY_CAPTURE, &MEDIATYPE_Video, pSrc, IID_IAMCrossbar, (void **)&pxBar);
    if (FAILED(hr))
    {
        CheckHR(hr, "Failed to get crossbar filter");
        goto done;
    }
}//if
else
{
    CheckHR(hr, "Failed to get crossbar (capture)");
    goto done;
}
LONG lInpin, lOutpin;
hr = pxBar->get_PinCounts(&lOutpin, &lInpin);
BOOL IPin = TRUE; LONG pIndex = 0, pRIndex = 0, pType = 0;
while (pIndex < lInpin)
{
    hr = pxBar->get_CrossbarPinInfo(IPin, pIndex, &pRIndex, &pType);
    if (pType == input)
    {
        break;
    }
    pIndex++;
}
BOOL OPin = FALSE; LONG pOIndex = 0, pORIndex = 0, pOType = 0;
while (pOIndex < lOutpin)
{
    hr = pxBar->get_CrossbarPinInfo(OPin, pOIndex, &pORIndex, &pOType);
    if (pOType == PhysConn_Video_VideoDecoder)
    {
        break;
    }
    pIndex++;
}
hr = pxBar->Route(pOIndex, pIndex);


done:
SafeRelease(&pPropBag);
SafeRelease(&pMoniker);
SafeRelease(&pxBar);

SafeRelease(&pGraph);
SafeRelease(&pBuilder);
SafeRelease(&pSrc);
return hr;

}